More than two dozen pro-government fighters were killed in northwestern Syria overnight in an attack by rebel forces, an activist group said on Tuesday.

The UK-based Syrian Observatory for Human Rights said the surprise offensive late on Monday targeted a pair of villages and observation points in the coastal province and government stronghold of Latakia, near the Turkish border.

"At least 27 regime forces and allied fighters, including eight officers, were killed in fierce clashes and shelling in the village of al-Ateira," said Observatory head Rami Abdel Rahman.

"They took al-Ateira and kicked out regime forces from several observation points after killing or wounding them."

Another 40 government loyalists were wounded and six rebels were killed, he said.

The death toll made the attack the bloodiest opposition assault on the area in three years, according to the Observatory.

In retaliation, the government and its ally Russia pounded rebel-held areas in Latakia and neighbouring Idlib, killing four civilians, the monitor group said.

Al-Ateira lies about two kilometres south of the Turkish border.

The Observatory said the opposition fighters included local rebels from Latakia as well as more hardline forces.

Latakia is a stronghold of Syrian President Bashar al-Assad and is home to the Hmeimim airbase, where Russian troops and warplanes have been based since 2015.

But forces opposed to Assad have repeatedly attacked the province.

They hold a northeastern sliver of territory bordering the neighbouring province of Idlib.

That area falls under a de-escalation deal agreed last year between Russia, fellow government backer Iran, and rebel ally Turkey.

The rebel attack came as the opposition in Syria's south has crumbled in the face of a pro-government assault, the latest rebel area to fall back under Damascus' rule.

Assad meeting

Speaking on Monday, Assad said his top priority was the reconstruction of his country, battered by more than seven years of fierce fighting.

He spoke during a gathering with his foreign minister, Walid Muallem, and other Syrian diplomats in Damascus, according to the presidency.

"Reconstruction is the top priority in Syria, backed up by the continued fight against terrorism," Assad said.

Syria's war began in 2011 with protests against Assad's rule that turned into an armed conflict.

Violence has gutted the country's infrastructure, including electricity and water systems, schools and hospitals, and other institutions needed for daily civilian life.

In 2017, the World Bank estimated the cost of war-related losses in Syria at $226bn, the equivalent of four times the country's pre-war gross domestic product.